Trevor Cook

The lockdown for me meant the longest time spent at home for many years − a welcome break and time to catch up on numerous things. Now the grazing rotation is running perfectly, the firewood shed full, an old shed is weatherproof, and the office is tidier.

In tidying my office I got captivated by old client reports, and shuddered at some. They were far too wordy, like little reference books. The font was too small and the typeface hard to read. However, it was the content that I was both impressed and embarrassed with. The reports were from the mid 1990s when drench resistance was an issue but the new combination drenches were dealing with that. Product inputs were prominent; the role of feeding was not as prominent.

The worm management advice was much the same as I would give today − drench testing, refugia, using combinations, and warnings about long-acting products. Grazing advice was focused on lowering the larval contamination challenge to lambs and calves and grazing plans took precedence over best feeding of young stock or making best use of feed.

I didn’t give as much advice then about modifying drench use on low contamination grazing and I have often wondered if that has been one of the big drivers of increasing drench resistance.

The old reports show the early development of management concepts that I promote strongly today. They were based on research that, over time, I have been able to validate by observing and measuring the outcomes on farms. Today’s advice has a more practical slant. All advice changes over time and, having attended a presentation about farming and greenhouse gases, I see a definite need for change.

Not as prominent in 1995 as today was my focus on young stock. Growing replacements well in all grazing systems was important but back then the links with subsequent production were not as clear. Hogget mating weights of 34kg was a target, and for a 55kg ewe that is above that so-called magical 60%.

I never believed that applied to lighter ewes. The long-term impact of ewe lambs reaching puberty was not evident in any of my reports and such discussion was all about the success of hogget lambing. Yearling heifer mating weights of 260kg appeared in one of the reports but mature cows, especially Angus, were smaller then − but not that small.

Even in deer herds the weights of yearling hinds were too light to allow high pregnancy rates.

Today, replacement females being too light is still a major limitation to achieving higher production. Averages are used rather than minimum weights. The size of the tail end determines the mob performance.

Advice on growing young stock for breeding or finishing hasn’t changed. They must have quality feed to grow fast and will always give the biggest return on investing in quality feed − hence the caution I always give about using just percentage of body weight for calculating feed demand. Offering more of a poorer feed will not make up for its lower quality unless stock have lots of choice in which case they will choose to eat only the highest quality. If made to eat more, their rate of weight gain will drop.

In my early reports animal health did dominate the advice so, when dealing with growing lambs or calves, worms and trace elements were very much to the fore. Both can have a huge impact on weight gains, so their dominating the advice was valid.

For worms, though, there is a real interaction between feed quality and quantity, and susceptibility. The impact of a relatively low larval challenge on growing calves on poor quality summer pasture is significantly more than with them on higher quality pasture.

In fact, the impact of worms is always much greater when animals are under feed pressure.

The impact of deficient trace elements varies: for calves, very low selenium levels even on very good feed will make them look wormy and not grow; lambs on very good grass with little clover can grow slowly if the soils are mildly low in cobalt.

But it is always wise to remember that if animals are not deficient they will not grow or perform any better with trace element supplements.